The long term objective of this study is to determine whether a genetic susceptibility factor for Alzheimer's disease (apolipoprotein xi4; APOE Xi4), predisposes head trauma victims to subsequent development of neurodegenerative disorders. The specific aim is to assess the relationship between possession of the APOE xi4 allele and recovery from acute head trauma. Separate lines of research have shown that both APOE- xi4 and a history of head trauma are associated with increased risk for development of Alzheimer's disease (AD). Further, evidence suggests that the risk attributable to APOE xi4 is greater in head trauma victims. Virtually every investigator who has speculated that head trauma is a risk factor for AD has cited the occurrence of dementia pugilstica, or chronic traumatic brain injury (cTBI), in boxers to support their theory. cTBI represents the extreme clinical endpoint of cumulative sports-related neurologic deficits, which manifests as progressive disturbances in motor, behavior, and cognitive functioning. Preliminary findings suggest APOE xi4 is also a risk factor for development of chronic traumatic brain injury in boxers. Boxers are an ideal model for the study of head trauma in that baseline assessment is obtainable and trauma can be quantified. The proposed study is a prospective cohort investigation of recovery from acute head injury in professional boxers. Boxers will complete a baseline neuropsychological battery and APOE genotyping. Post-bout changes in cognitive functioning will be assessed at one day, one week and one month following active competition. Genotype-specific recovery (i.e., presence or absence of the xi4 allele) will be measured in terms of return to baseline on neuropsychological testing. Potential applications of this research include advancing our understanding of genetic risk factors for the brain's response to trauma and development of neurodegenerative disorders as well as objectifying safety standards in high risk sports.